Hard disk drive incorporating rotating magnetic disks is commonly used for storing data in the magnetic media formed on the disk surfaces, and a movable head are generally used to read data from and write date into tracks on the disk surfaces.
Nowadays, the magnetoresistive (MR) read heads are widely used in a popular magnetic head because a MR element with higher sensitivity is included therein. A plurality of performance of a magnetic head must be tested before the magnetic head is used, which includes anti-high temperature performance, dynamic flying height (DFH) performance, Signal-to-Noise Ratio (SNR) performance, reliability, stability and the like. For example, a magnetic head with a bad anti-high temperature performance will represent a lot of noise if used under a high temperature condition. And a magnetic head having a bad SNR performance will damage the reading stability of the magnetic head and affect the reading performance finally. Thus, the testing of the performance of the magnetic head is quite important and necessary.
The following method has been used as a conventional method of testing a MR read head. As shown in FIG. 1, the MR read head 10 includes two hard magnets 112, a MR element 114 sandwiched between the two hard magnets 112, and two shielding layers 116 disposed on both sides of the MR element 114 and the hard magnets 112. As known, the resistance of the MR element varies with the changes of an external magnetic field, which results in variation in the output of the MR read head. Thus an operation that applies a magnetic field in a direction 19 that is parallel to the shielding layers 116 and at 0° angle to the air bearing surface 117 (ABS) of the MR read head 10 (hereinafter this is referred to as “common magnetization direction”) and measures the output voltage of the MR read 10 head is repeatedly carried out. And the difference between the highest and lowest output voltage is calculated as the variation and used to evaluate whether the output variation is within a certain allowable value. Therefore, the tested magnetic head will be rejected as a defective magnetic head if the output variation is beyond the allowable value.
The above-mentioned method utilizing the common magnetization direction is widely used in the testing of DFH performance, SNR performance, the reliability and the stability of the magnetic head. However, the testing by using the common magnetization is limited since the performance requirement of the magnetic head become higher and higher. Thus, the testing method is limited to a degree. With regard to the anti-high temperature testing, there is little sensitivity responding to the magnetization with the common magnetization direction, however. Thus, methods of testing the anti-high temperature for the magnetic head are still under development.
US patent publication No. 20080049351 A1 discloses a testing method of the anti-high temperature for the magnetic head. As shown in FIG. 2, a heating element 35 is provided on an element formation surface 2101 of the magnetic heads 21, so as to applying heat and stress to the MR element 32 of the magnetic head 21. Concretely, the heating element 35 generates heat when electric current is passed through it. A large internal stress is generated in the MR element 32 due to the thermal expansion of the MR element 32 caused by heat generated by the heating element 35 and the thermal expansion of the material surrounding the MR element 32, in addition to internal distortion inherent in the MR element 32. The level of noise that occurs in an output of the MR element 32 is measured under these conditions to identify whether or not the magnetic head 21 has a potential distortion that can cause noise under high-temperature conditions.
However, since the magnetic head is tested under a plurality of changing high-temperature conditions repeatedly, thus the selection and controlling of the sample temperature need to be precise. If the temperature is too high, there is a potential of damaging the non-defective magnetic head during the testing.
Moreover, this method mentioned above is only suitable for the magnetic head with a heating element equipped therein. The anti-high temperature testing is incapable of being performed in the case that the heating element is failed to be equipped in the magnetic head.
Hence, it is desired to provide an improved method of testing anti-high temperature performance of a magnetic head, and a method of testing the performance of a magnetic head to overcome the above-mentioned drawbacks.